[ale] Linux and routes

[Andrew Newton]

I've got a network setup as such:

                   dedicated ISDN
                      to ISP
                        |
                        |
                  -------------
                  | router    |
                  -------------
                        |
  --------------------------------------
        |                           |
    ---------                    ---------
    | Linux |                    | Notes |
    ---------                    ---------
        |                           |
  ---------------------------------------
                   |
             internal LAN

Both the Linux box and the Notes box (running NT) have
two NIC's, one on each network, but neither are routing IP.
The Linux box receives all incoming mail, keeping mail
for users defined on it and relaying mail to the Notes
box for users in the domain that it doesn't know about.
The Notes box also runs the Domino web server and the Notes
Web Retreiver.

For reasons too many to explain, we want to rid ourselves
of the Notes Web Retriever task and use Apache's proxy
service on the Linux box.  At the same time, we want to
add a second ISDN line to help with bandwidth problems
(I know whe should be using fractional T1, but there are
office politics involved here).  The second ISDN line will
be a dial-up.  So essentially, the dedicated ISDN will be
for incoming web and mail, and the dail-up ISDN will be
for outgoing web.  Both ISDN lines will be serviced by
individual ISDN routers.

So here's my question:  If I add another route to the
Linux box so it knows about both ISDN routers, does the
Linux kernel keep track (I guess a routing table) of where
the traffic came from?  In other words, if a TCP connection
initiates through the dedicated side, will the Linux box
respond via that route or will it respond using the dial-up
router?

-- 
Andrew Newton
lfs at eskimo.com 
www.eskimo.com/~lfs